Contact lenses of various types are being manufactured and used for correcting vision, cosmetic purposes and therapeutic purposes, among others. Such contact lenses may be broadly classified as being printed contact lenses or clear contact lenses.
A contact lens, being an object that is worn on the eyes, which are known to be sensitive organs, is manufactured such that it meets a stringent technical specification. To ensure that the contact lenses meet the strict quality requirements of the consumer, they are inspected at various stages of their manufacture.
Traditionally, a contact lens, after being molded, is inspected for defects, using bright-field illumination. FIG. 1 illustrates an image 100 of a clear contact lens, which is taken using bright-field illumination. In the figure, the bright area is the contact lens, and the black dots 102 are bubble defects, or other types of defects, that are present in the clear contact lens. While the bright-field illumination is well suited for inspecting clear contact lenses, such a technique may not be best suited for inspecting printed contact lenses. A printed contact lens has an iris print, and when such lenses are illuminated using bright-field illumination, the image of the printed contact lens will include a black area corresponding to the iris print, and black dots corresponding to bubble or other types of defects. Such an image may not be suited for identifying the defects because the black dots corresponding to the bubble defects may get camouflaged in the black area corresponding to the iris print. Alternatively, if only dark-field illumination is used for inspecting the printed contact lens, the image of the printed contact lens will include bright areas corresponding to the iris print and bright dots corresponding to bubble or other types of defects. Such an image may not be suited for identifying the defects because the bright dots corresponding to the bubble or other similar type of defects may get camouflaged in the bright area corresponding to the iris print. Hence, there is a need in the industry for a system that can reliably identify the defects in a printed contact lens.
Further, in the traditional techniques, during the process of capturing images for defect detection, systems may require one of the molds (male or female) in the mold assembly to be removed to provide access to the inspection system for illuminating the contact lens to perform defect inspection. When the molds are disengaged, there is a possibility of defects being introduced during the disengagement process. Further, when defects are found in the contact lens, it will be difficult to determine if the defects were created during the molding process or during the disengagement process. Hence, there is a need in the industry to understand the process-related defects at the point of their creation, so that appropriate measures can be taken to address the problem.